Hybrid RANS/LES Simulations for Aerodynamic and Aeroacoustic Analysis of a Multi-Element Airfoil

Abstract

A hybrid RANS/LES modeling approach is used for simulating the turbulent flow around a three-element airfoil in high-lift configuration. A detailed analysis of the flow is made, based on the simulation outcome. A comprehensive aeroacoustic analysis involving all three elements of the airfoil is also presented. To provide input data for acoustic analogies, the results of the simulation are sampled at a permeable stationary surface near the airfoil and at the airfoil itself. The far-field noise signature of the high-lift airfoil is computed with the help of the Kirchhoff integral surface method, the Ffowcs-Williams and Hawkings method for a stationary, permeable surface, and the Curle method. The sound pressure level spectrum exhibits a broadbanded shape with several narrow-banded tonal peaks at low Strouhal numbers. The broad-banded peak at high Strouhal numbers, which is typically associated with vortex shedding behind the blunt slat trailing edge, was also captured. Using Curle's acoustic analogy, the noise emission pattern of the three elements is explored, isolated from each other, revealing that both slat and flap act as dipoles. By refining the used grid, the flow results are significantly improved in terms of slat shear layer instability and resolved turbulent content as compared to our previous work.

A time-domain Kirchhoff formula for the convective acoustic wave equation

“…Consequently, the FW-H equation is not appropriate for all types of wave propagation. In practical CAA problems, the Kirchhoff approach finds wide application to aerodynamic noise generation involving high-lift devices [4,5], rotors [3,[6][7][8][9] and jet flows [10][11][12][13][14].…”